Biogenic volatile organic compounds (BVOCs) emitted from tropical
rainforests comprise a substantial fraction of global atmospheric VOC
emissions, however there are only relatively limited measurements of these
species in tropical rainforest regions. We present observations of isoprene,
&alpha;-pinene, camphene, &Delta;-3-carene, &gamma;-terpinene and
limonene, as well as oxygenated VOCs (OVOCs) of biogenic origin such as
methacrolein, in ambient air above a tropical rainforest in Malaysian Borneo
during the Oxidant and Particle Photochemical Processes above a south-east
Asian tropical rainforest (OP3) project in 2008. Daytime composition was
dominated by isoprene, with an average mixing ratio of the order of ~1 ppb. &gamma;-terpinene, limonene and camphene were the most abundant
monoterpenes, with average daytime mixing ratios of 102, 71 and 66 ppt
respectively, and with an average monoterpene toisoprene ratio of 0.3 during sunlit hours, compared to 2.0 at night. Limonene and camphene
abundances were seen to be related to both temperature and light conditions.
In contrast, γ-terpinene emission continued into the late afternoon/evening, under relatively low temperature and light conditions.
The contributions of isoprene, monoterpenes and other classes of VOC to the
volatile carbon budget and OH reactivity have been summarised for this
rainforest location. We observe good agreement between surface and aircraft
measurements of boundary layer isoprene and methacrolein above the natural
rainforest, suggesting that the ground-level observations are broadly
representative of isoprene emissions from this region.